优化事件实现
上述的事件实现并没有优化性能。此实现为每个委托实例生成一个字段，当控件上定义了很多事件时，就会增加存储成本。基类 System.Web.UI.Control 为存储和检索事件委托提供了更有效的数据结构（通过其 Events 属性）。Events 属性的类型为 EventHandlerList，该类型是为有效存储和检索事件委托而设计的数据结构。下面的示例说明了使用 Events 属性的事件实现。此 C# 示例与本主题前面定义的 MyButton 示例只在其 Click 事件的实现上有所不同。实现此事件的代码用粗体突出显示。
注意 此版本的 Visual Basic .NET 不支持事件属性。
[C#]
using System;
using System.Web.UI;
namespace CustomControls
{
public class OptimizedEventButton: Control, IPostBackEventHandler
{
// Defines a key for storing the delegate for the Click event
// in the Events list.
private static readonly object ClickEvent = new object();
// Defines the Click event using the event property syntax.
// The Events property stores all the event delegates of
// a control as name/value pairs.
public event EventHandler Click
{
// When a user attaches an event handler to the Click event
// (Click += myHandler;), the Add method
// adds the handler to the
// delegate for the Click event (keyed by ClickEvent
// in the Events list).
add
{
Events.AddHandler(ClickEvent, value);
}
// When a user removes an event handler from the Click event
// (Click -= myHandler;), the Remove method
// removes the handler from the
// delegate for the Click event (keyed by ClickEvent
// in the Events list).
remove
{
Events.RemoveHandler(ClickEvent, value);
}
}
// Invokes delegates registered with the Click event.
//
protected virtual void OnClick(EventArgs e)
{
// Retrieves the event delegate for the Click event
// from the Events property (which stores
// the control's event delegates). You must
// cast the retrieved delegate to the type of your
// event delegate.
EventHandler clickEventDelegate = (EventHandler)Events[ClickEvent];
if (clickEventDelegate != null) {
clickEventDelegate(this, e);
}
}
// Method of IPostBackEventHandler that raises change events.
//
public void RaisePostBackEvent(string eventArgument)
{
OnClick(new EventArgs());
}
protected override void Render(HtmlTextWriter output)
{
output.Write("<INPUT TYPE = submit name = " + this.UniqueID +
" Value = 'Click Me' />");
}
}
}
注意 为简单起见，本文档中的一些其他示例使用事件字段来定义事件。但是，在您的控件中，应该使用此处讨论的优化实现。
